After working inside your systemPower supply unitsYour system supports one of the following:• Two 495 W, 750 W, or 1100 W AC power supply units (PSUs)• Two 1100 W DC PSUs• Two 750 W mixed mode PSUsCAUTION: For AC PSUs, use only PSUs with the Extended Power Performance (EPP) label on theback. Mixing PSUs from previous generations of systems can result in a PSU mismatch conditionor failure to turn on.NOTE: Titanium PSU is nominally rated for 200 V AC to 240 V AC input only.NOTE: When two identical PSUs are installed, power supply redundancy (1+1 – with redundancy or2+0 – without redundancy) is configured in system BIOS. In redundant mode, power is supplied tothe system equally from both PSUs when Hot Spare is disabled. When Hot Spare is enabled, one ofthe PSUs will be put into standby when system utilization is low in order to maximize efficiency.NOTE: If two PSUs are used, they must be of the same maximum output power.Hot spare featureYour system supports the hot spare feature that significantly reduces the power overhead associated withpower supply redundancy.When the hot spare feature is enabled, one of the redundant PSUs is switched to the sleep state. Theactive PSU supports 100 percent of the load, thus operating at higher efficiency. The PSU in the sleepstate monitors output voltage of the active PSU. If the output voltage of the active PSU drops, the PSU inthe sleep state returns to an active output state.If having both PSUs active is more efficient than having one PSU in the sleep state, the active PSU canalso activate the sleeping PSU.The default PSU settings are as follows:• If the load on the active PSU is more than 50 percent, then the redundant PSU is switched to theactive state.• If the load on the active PSU falls below 20 percent, then the redundant PSU is switched to the sleepstate.You can configure the hot spare feature by using the iDRAC settings. For more information about iDRACsettings, see the Integrated Dell Remote Access Controller User’s Guide available at Dell.com/idracmanuals.Removing the power supply unit blankIf you are installing a second power supply unit (PSU), remove the PSU blank in the bay by pulling theblank outward.158
